1. Field of the Invention
The present invention relates generally to a mechanical locking system and particularly to a brake-transmission interlock system (BTSI) for a motor vehicle.
2. Description of the Related Art
Locking arrangements for selector levers of a motor vehicle transmission have been required in. U.S. vehicles for a substantial number of years. The purpose of these devices is to prevent accidental engagement of the vehicle. Relatively more recently, regulations have required systems where the operator must engage the braking mechanism before moving the selector lever to the desired gear.
Traditionally, vehicles having these types of brake-transmission interlock systems must be moved out of a neutral position (parking or neutral) into a driving position in order to be able to drive the vehicle. The vehicle may start to drive, although this is not intended, when, while the engine is running, the selector lever is inadvertently moved from the neutral position into a driving position. An unattended abrupt acceleration may also occur during the warmup phase of the engine, when the idling speed is increased and the selective lever is brought into a driving position.
In order to avoid such circumstances, it is known to provide a locking arrangement for the selector lever, particularly for automatic vehicle transmissions, in which a locking member locks the selector lever when the brake is not operated. The locking member engages in corresponding indentations of an adjustable pawl so that the selector level is locked in the neutral position (parking or neutral).
U.S. Pat. No. 5,379,872 discloses a locking assembly for an automatic transmission selector lever which includes a locking member arranged on the selector lever, and an adjustable pawl. The adjustable pawl has indentations into which the locking member engages when the brake is not operated so that the selector lever is locked in the neutral position. The pawl has steeply extending flanks which bound the indentations where the locking member rests when the selector lever is locked and an actuating force is applied to the selector lever. The actuating force is introduced into the flanks of the pawl via contact surfaces of the selector lever at a contact point of the flanks. The flanks provide a substantially horizontal force component and a substantially vertical force component of the actuating force. As a result, the locking arrangement permits a secure unlocking when there are high operating forces on the locked selector lever. Contact in this manner, the actuating force applied to the selector lever is introduced in the pawl. On the steep flanks, the introduced force is transferred into an almost horizontal component pointing in the direction of the pivot of the pawl and into a downward-directed component which acts as an almost vertical supporting force. In this case, the steep flanks have the effect that the supporting force is a low range which is clearly exceeded by the horizontal component. As a result, the supporting force can act upon the components holding the pawl in the locked position only with a low power. As a result, the components can be removed from the pawl by low forces, whereby the pawl, while unlocking the selector lever, disengages from the locking member.
U.S. Pat. No. 4,817,405 discloses a lock for an automatic transmission shifter lever which prevents the transmission of the vehicle from being inadvertently shifted out of the parked position while the vehicle is running. In that particular invention, a sleeve or collar is received about a steering column in the vehicle. Mounted on the sleeve is a gear shift lever which can be selectively manipulated to select the desired gear. As the gear shift lever is manipulated, the sleeve or collar rotates about a central shaft of the steering column. A lock, including a rotatable lock cylinder, is mounted near the gear shift lever in the outer casing of the steering column. The lock extends inwardly and adjacent the sleeve or collar. A flange or ear extends radially from the lock cylinder and can be rotated between a free and locked position only by the aid of a key which will operate the lock. The sleeve or collar includes a receiving slot which, when the gear shift lever is moved to the park position, is adjacent the extending flange or ear of the lock. The flange or ear can thus be rotated into the slot by the key to the lock thereby preventing accidental manipulation of the gear shift lever out of the park position.
U.S. Pat. No. 4,610,336, an automatic transmission locking mechanism is disclosed which includes a lever rotatively interlocked with a manual shift lever, a rod adapted to be advanced or retracted by the lever, a parking gear, a pawl having a detent to be engaged with the parking gear, a cam moved on the rod for pushing up the pawl with a detent in shifting the manual shift lever to the parking position, a bracket on which the cam runs and a spring for releasing the pawl from the parking gear and to retain the pawl at the released position. The pawl is adapted to be turned on a pawl shaft, and a plate-shaped clamp is fitted in a grove formed in the pawl shaft at the free end thereof to restrain the actual movement of the pawl. The clamp is fixed to a case with a bolt with a spring disposed nearby the free end of the pawl and the sleeve can easily be fitted on or removed from the pawl shaft by fastening or removing, respectively the bolt fixing the clamp. Other examples of transmission locking mechanisms can be found in U.S. Pat. Nos. 4,585,103; 4,252,219; 4,033,158; 3,960,235; 3,948,339; and 3,939,939.
A significant disadvantage with substantially all of the aforementioned transmission interlock systems is they often require complicated mechanical linkages and assemblages or electrical circuits and solenoids to engage or disengage the pawls locking the transmission shifter in place. The purpose of the invention is to produce a reliable brake transmission interlock system requiring fewer components and resulting in a less costly assembly.
According to one form of the invention, a brake transmission interlock system for a transmission shifter assembly is provided which includes a selector lever cooperating with at least one linking lever such that the movement of the selector lever results in a corresponding movement of one of the linking levers to select a desired gear. An assembly for selectively locating the lever at a desired gear selection position is provided in association with at least one fluid locking assembly cooperating with the locating assembly to lock the selector lever in a desired position, preventing accidental disengagement. The fluid locking assembly includes at least one linear actuator whose movement is controlled by a magneto rheological fluid.
In another form of the invention, a transmission shifter assembly includes a selector lever having a first end and a second end, the second end interconnected to at least one linking lever such that the movement of the first end of the selector lever results in a corresponding movement of the linking lever. A positioning plate is located adjacent the base of the selector lever and includes at least one aperture configured to receive a locking assembly associated with the selector lever to selectively fixing a location of the lever. Connected to the locating assembly is at least one fluid locking member which selectively permits movement of the locating assembly with respect to the aperture. In further embodiment of the invention, an assembly is provided which cooperates with the lever to produce a magnetic field about the fluid locking member when the selector lever is in a predetermined position. Additionally, at least one of a braking operation and a key operation cooperates with the magnetic field assembly to selectively lock and unlock the fluid locking member.
In yet another form of the invention, the transmission shifter assembly includes a lever having a lower end coupled to at least one linking lever such that the movement of the lever assembly results in a movement of the linking lever to select a desired gear. A pawl is attached to the lower end of the lever assembly and is moveable between a first and second position. Connected to the pawl is an actuator assembly configured to selectively move the pawl between a first and second position. Adjacent the lever is a positioning plate having a plurality of detents configured to receive at least a portion of the moveable pawl to selectively fix a position of the lever assembly. In still a further form of the invention, at least one of the braking operating and key operation cooperates with the actuator assembly to selectively lock and unlock the actuator assembly.
In the most basic form of the invention, a magneto rheological fluid locking member comprises the principal element of the brake transmission interlock system, providing the interconnecting element between the locking pawl of the shifter assembly and a release button engaged by the operator. The magneto rheological fluid locking member cooperates with at least one of a braking operation and key operation to selectively engage and disengage a magnetic field which alters the operational characteristics of the assembly.